A) Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing a semiconductor device, and, more particularly, to a semiconductor device having an insulation film of a high dielectric constant and a method of manufacturing the semiconductor device.
B) Description of the Related Art
Insulated gate (IG) field effect transistors (FETs), typical examples of which are MOS transistors, are widely used as typical semiconductor devices used in a semiconductor integrated circuit device. For a larger scale integration of semiconductor integrated circuit devices, IG-FETs have been miniaturized according the scaling law. Miniaturization reduces the sizes of IG-FETs, such as making the gate insulation film thinner and shortening the gate length, to improve the performances of miniaturized devices while keeping the normal performances.
A MOS transistor has a silicon gate electrode on a gate oxide film. The silicon gate electrode is doped with n-type impurity such as phosphor (P) or arsenic (As), or p-type impurity such as boron (B). As the gate oxide film becomes thin, there occurs a phenomenon that the impurity in the gate electrode penetrates through the gate oxide film, and diffuses into the underlying channel region. When the impurity in the gate electrode diffuses into the channel region, it lowers the threshold voltage of the transistor, and causes punch-through. Especially, the penetration of boron in the p-channel transistor is of problem.
It is known that introduction of nitrogen in the gate oxide film is effective for preventing penetration of boron. Nitrogen can be introduced into the gate oxide film, for example by conducting thermal nitridation after forming a gate oxide film by thermal oxidation.
The gate insulation films of MOS transistors of the next generation should be made as thin as 2 nm or less. With that film thickness, the tunnel current starts flowing, the gate leak current becomes uncontrollable, and an increase in power dissipation cannot be avoided. To suppress the tunnel current which flows through the gate insulation film, the gate insulation film in use should be thick.
To increase the physical thickness of the gate insulation film while keeping the equivalent thickness of the gate insulation film based a silicon oxide film at most 2 nm, the use of a high specific-dielectric-constant insulation material having a dielectric constant higher than that of a silicon oxide for the gate insulation film has been proposed.
Japanese Patent Laid-Open Publication No. 2001-274378 proposes the use of barium titanate (Ba(Sr)TiO3), titanium oxide (TiO2), tantalum oxide (Ta2O5), zirconium oxide (ZrO2), hafnium oxide (HfO2), silicon nitride (Si3N4), or alumina (Al2O3), which has a specific dielectric constant higher than that of silicon oxide, for a gate insulation film. The publication also proposes a structure where a silicon oxide film is intervened between such a high specific-dielectric-constant insulation film and a silicon substrate.
The use of a new material having a high specific dielectric constant for the gate insulation film of an IG-FET brings about a new problem. Solving such a new problem is desired to promote the practical use of new materials.